Brown / Grizzly Bear Facts

Grizzly cubs

Taxonomy: While there has been much confusion about the taxonomy of brown bears (Ursus arctos), taxonomists agree there are at least two subspecies in North America — the grizzly bear (U. a. horribilis) and the Kodiak bear (U. a. middendorffi). There is confusion about whether to consider others, like U. a. gyas and U. a. macfarlani, as separate subspecies.

The Kodiak bear has lived separately on Kodiak, Afognak, and Shuyak Islands in southwestern Alaska for thousands of years with no interbreeding with other populations. However, there is no such geographic demarcation between the coastal U. a. gyas and the inland U. a. horribilis. There is a continuum of difference between the larger coastal brown bears and the interior individuals that are generally called grizzly bears. Coastal brown bears have a greater amount of animal protein in their diet, achieve larger size, and have slight differences in coloration. At any point from the coast to the interior there is interbreeding between the populations (Jonkel 1987, p 456-473).

Home Range: Grizzly bears can be found in the Canadian provinces of British Columbia, Alberta, Yukon, and the Northwest Territories; and the US states of Alaska, Idaho, Wyoming, Washington, and Montana. In general their home range is between 10 and 380 square miles. A grizzly bear’s home range is basically inland – away from major bodies of water. In most cases, a grizzly bear’s home range includes an area of forested land or shrub cover, which is used mostly for escape (Jonkel 1984, p 21).

Grizzly on shore

Food Types: Grizzly bears feed on berries (blueberries, bearberries, etc.), roots, bulbs of plants, ground dwelling rodents, and most importantly whitebark pine nuts. Sometimes grizzlies will locate a cache of these nuts that a ground squirrel has stored for the winter. With their excellent sense of smell, grizzlies can locate carrion from miles away and will readily feed on it (Bauer and Bauer 1996, p 62).

Grizzlies may also prey on moose, elk, mountain goats and mountain sheep. During the spring months, grizzlies also feed on the calves of these animals (Jonkel 1984, p 23).

Another major food source for grizzlies are army cutworm moths. During the summer months in the Yellowstone area, these moths congregate on sub-alpine plants located above the timberline at elevations higher than 10,000 feet. During the early morning hours these moths drink nectar and then during the day they cluster on the surrounding rocks. Grizzlies from all around climb to these high elevations to consume 10,000 to 20,000 of these moths a day. At times like this, when food is abundant, numerous grizzlies will congregate and feed together. Once the food source is depleted, the grizzlies will go their separate ways in search of other food (Bauer and Bauer 1996, p 67).

Kodiak bears generally rely on the same types of food as grizzlies, with one addition. Living in coastal areas provides these bears with a rich supply of protein. These coastal areas are so rich in salmon that a 40% higher density of brown bears can be supported there (Bauer and Bauer 1996, p 97).

Paws: Grizzly bear paws are black or brownish in color with wrinkled skin on the pad (Brown 1993, p 73).

Shoulder Hump: Brown bears have a distinguishing shoulder hump. This hump is actually a mass of muscle, which enables brown bears to dig and use their paws as a striking force (Brown 1993, p 77).

Grizzlies wrestling

Claws: Brown bear claws are long and curved, ranging in color from yellow to brown. In rare cases grizzlies have been observed with white claws. These claws are used to dig up roots and bulbs of plants as well as to excavate den sites (Brown 1993, p 74).

Tracks: The toes fall close together and nearly in a straight line in a brown bear track. The toe pads are generally touching each other with the smallest toe on the inside of the track. Impressions from the fore claws are usually found far in front of the toes because the claws are twice as long as the toe pads. The front tracks of brown bears measure 6-8 inches long (excluding heel) and 7-9 inches wide. Hind tracks measure 12-16 inches long and 8 to 10 ½ inches wide (Brown 1993, p 76).

Coloration: Grizzlies range in color from white, blonde, brown, black and shades thereof. The tips of most fur are lighter in color giving them a grizzled effect (Brown 1993, p 65).

Growth and Development: Brown bears can weigh 150-200 pounds at the end of their first year of life. They reach sexual maturity between 4 and 5 years and are considered fully grown by 8 to 10 years of age (Brown 1993, p 139).

Weight: Females reach their maximum weight of 270 to 770 pounds in 8 years. Males reach their maximum weight of 330 to 1150 pounds in 12 years. The heavier a female is the better are her chances of having cubs. The heavier a male is the better chance he has of successfully breeding with a female. Males are 1.2 to 2.2 times as heavy as females.

Making a Living: In general, brown bears will flee as soon as they detect humans. Finding food, finding mates, and avoiding being preyed upon govern a brown bear’s life (Stirling 1993, p 91).

Grizzly mom and cub

Most brown bears are active during the morning and early evening hours. During the daytime they rest in day beds, often constructed in dense cover to escape the heat. During the late summer and fall months, when they are fattening up for the long months of hibernation, brown bears may be active throughout the day. As food items become scarce, the brown bear’s territory increases. Within their home range, brown bears use a wide variety of habitats. Brown bears travel from alpine food sources to estuaries, to berry patches, to salmon spawning sites – visiting each site when its particular food source is available (Stirling 1993, p 92-93).

Dens: Dens must provide protection and security during the winter months. Brown bears can excavate a den but often use rock caves and hollow trees. Dens are dug in dry, stable soil where winter temperatures will remain above freezing. Usually the den site terrain is sloping. As snow falls it covers and helps to insulate the den. Generally the den is just large enough to accommodate the bear. The entrance to the den leads to a tunnel that slopes downward to the actual sleeping chamber. This sloping tunnel allows stale air to escape. Most dens are used only once. Occasionally a den built in unstable ground will collapse (Stirling 1993, p 94).

Mating: Females generally are first able to reproduce between 4 ½ and 10 years of age. The number of cubs in a litter depends upon the female’s body weight. Mating occurs between early May and mid July with cubs born between the end of January and early March. Usually a female brown bear reproduces once every 3 to 5 years (Brown 1993, p 132, Bauer and Bauer 1996 p 94). Since only 1 in 3 females breed in a given year, males must range widely in order to find a mate (Stirling 1993, p 92-93). A mother brown bear will remain with her young for 1 ½ to 3 ½ years (Brown 1993, p 145).